Buoyancy assist tool

Abstract

A system includes a casing string and a buoyancy assist tool that is disposed in the casing string. The buoyancy assist tool includes a tubular body, a wiper plug assembly, and a degradable member. The wiper plug assembly is disposed inside the central passageway of the tubular body, and the degradable member retains the wiper plug assembly to the tubular body.

What is claimed is: 
     
       1. A method comprising:
 running a tubing string comprising a tool inside a wellbore, the tool comprising a wiper plug assembly disposed within a body of the tool, the tool being configured to form a fluid barrier inside a central passageway of the tubing string; 
 providing the wiper plug assembly with a tubular member having a diameter selected to establish an annular space between the tubular member and the body; 
 using a degradable material extending radially inward from the body to the tubular member so as to sealably secure the wiper plug assembly to the body of the tool; 
 pressurizing the tubing string to breach the fluid barrier; 
 communicating a cement slurry into the tubing string and through the breached fluid barrier; 
 communicating another plug assembly into the tubing string behind the cement slurry; 
 chasing the other plug assembly with a completion fluid column until the other plug assembly enters and is fully enclosed within a central passageway of the tubular member of the wiper plug assembly; and 
 increasing pressure of the completion fluid column against the tool to release the wiper plug assembly and the other plug assembly from the degradable material and thus from the tool while leaving at least a portion of the degradable material in the tool for subsequent degradation. 
 
     
     
       2. The method of  claim 1 , wherein using the degradable material to secure the wiper plug assembly to the body of the tool comprises:
 forming the degradable material into a degradable member of a desired shape to secure the wiper plug assembly; 
 retaining the degradable member inside the body, the degradable member being radially disposed between the wiper plug assembly and the body; and 
 securing the wiper plug assembly to the degradable member using at least one shear member. 
 
     
     
       3. The method of  claim 2 , wherein retaining the degradable member inside the body comprises:
 securing the degradable member against a restriction formed in the body. 
 
     
     
       4. The method of  claim 1 , further comprising:
 following the cement slurry with the released wiper plug assembly; and 
 landing the released wiper plug assembly in a landing collar of the tubing string. 
 
     
     
       5. A system comprising:
 a casing string; and 
 a buoyancy assist tool disposed in the casing string, the buoyancy assist tool comprising:
 a tubular body comprising a central passageway; 
 a wiper plug assembly disposed inside the central passageway of the tubular body, the wiper plug assembly having a tubular member with a diameter selected to establish an annular space between the tubular member and the tubular body; 
 a cementing plug assembly for entering and being fully enclosed within a central passageway of the tubular member of the wiper plug assembly, the cementing plug assembly entering the casing string following a cement slurry through the central passageway, and being followed by a column of completion fluid; and 
 a degradable material in the form of an annular member to retain the wiper plug assembly to the tubular body, the annular member positioning the tubular member to maintain the annular space while enabling a seal between the tubular member and the tubular body. 
 
 
     
     
       6. The system of  claim 5 , wherein the casing string further comprises:
 a landing collar to receive the wiper plug assembly after the wiper plug assembly is released from the tubular body of the buoyancy assist tool. 
 
     
     
       7. The system of  claim 5 , further comprising:
 a shear member to releasably secure the wiper plug assembly to the degradable member. 
 
     
     
       8. The system of  claim 7 , wherein the shear member releasably secures the tubular member of the wiper plug assembly to the degradable member. 
     
     
       9. The system of  claim 5 , wherein the wiper plug assembly comprises a tubing comprising a central passageway, the apparatus further comprising:
 a removable fluid barrier to block fluid communication through the central passageway of the wiper plug assembly. 
 
     
     
       10. The system of  claim 9 , wherein the removable fluid barrier comprises a rupture disc. 
     
     
       11. The system of  claim 5 , wherein the tubular body comprises a restriction, and the degradable member has an outer dimension to cause the degradable member to be retained by the restriction. 
     
     
       12. The system of  claim 11 , wherein the restriction is disposed on a first axial end of the degradable member, the apparatus further comprising a locking ring disposed on a second axial end of the degradable member, the locking ring adapted to form a connection with the tubular body. 
     
     
       13. The system of  claim 5 , further comprising connectors to couple the tubular body to a tubing string. 
     
     
       14. A method comprising:
 running a casing string comprising a buoyancy assist tool inside a wellbore, wherein the buoyancy assist tool comprises a wiper plug assembly retained in place inside the buoyancy assist tool by a degradable sleeve and shear pins attaching the wiper plug assembly to the degradable sleeve, and the wiper plug assembly comprising a tubular member having a central passageway blocked by a first fluid barrier; 
 pressurizing the tubing string to breach the first fluid barrier; 
 communicating a completion fluid downhole inside the casing string to cause the fluid to circulate through the casing string and into an annulus between the casing string and the wellbore; 
 communicating a predetermined volume of a cement into the tubing string; 
 communicating a completion fluid column inside the tubing string following the cement, including communicating a cementing plug assembly to land inside and be fully enclosed within the central passageway of the tubular member of the wiper plug assembly; 
 pressurizing the tubing string to shear the shear pins to cause the wiper plug assembly and the cementing plug assembly to be released from the degradable sleeve; 
 allowing at least a portion of the degradable sleeve to remain in the buoyancy assist tool for subsequent degradation; and 
 using the wiper plug assembly with the cementing plug assembly fully enclosed therein to follow the cement through a central passageway of the casing string until the wiper plug assembly with the cementing plug assembly lands in a landing collar of the casing string. 
 
     
     
       15. The method of  claim 14 , further comprising:
 running equipment through the buoyancy assist tool, comprising allowing the degradable sleeve to degrade and be removed from the buoyancy assist tool.